European patent EP 339669 describes the preparation of Dolasetron I
by means of a method that includes as its last step the reaction between the 5-hydroxy-8-azatricyclo[5.3.1.03,8]-undecan-10-one (compound II) and the mixed anhydride formed from indole-3-carboxylic acid (compound III) and trifluoroacetic anhydride:

European patent EP 266730 (equivalent to Spanish patent ES 2061469) describes the preparation of compounds analogous to Dolasetron, also using the esterification described above as the last step.
These patents nevertheless present disadvantages. For example, in order to obtain compound II it is necessary to use protective groups that lengthen the synthesis route and entail a reduction of atomic efficiency. Moreover, the chosen protective group (Tetrahydropyranil, THP) leads to a mixture of diastereoisomers instead of to a single product. Also, the handling and purification of said intermediate product may prove to be complicated if carried out at industrial scale, as said mixture is an oil.
Another notable disadvantage is that column chromatography is used to carry out the purification of this mixture of diastereoisomers, while other methods of purification such as crystallisation or distillation are not possible. This becomes complicated if the product is to be prepared at industrial scale, and, combined with the atomic efficiency reduction remarked upon above, entails a considerable increase of residues and the attendant environmental problem.
Furthermore, the preparation of 5-hydroxy-8-azatricyclo[5.3.1.03,8]-undecan-10-one (compound II) includes a process of extraction of the product from the aqueous phase with ethyl acetate, in an operation that calls for the use of continuous-process extraction for considerable lengths of time (20 h), due to the high solubility of the compound in water. This operation requires specific installations which, although possible at industrial scale, means that the equipment needed to obtain the final product is more expensive.
Therefore, there remains a need for a method of obtaining Dolasetron which is applicable at an industrial scale, with fewer steps and which is more advantageous in terms of productivity, efficacy and minimisation of residues.